In order to provide industrial devices with high performance and high function, servo systems to drive the industrial devices have been improved to enhance maintenance properties, response properties, digitalization and accuracy. Furthermore, the servo systems have been downsized and wirings installed in the servo systems have been reduced.
In stators incorporated into the servo motors, space factors of slots of windings have been improved by conducting concentrated winding on division cores round which it is easy to conduct winding work. By adopting rare earth magnets, the rotors are downsized. A technique of using multiple layer printed wiring boards for conducting connection work of the concentrated windings is disclosed, for example, in Japanese Patent Unexamined Publication No. 2000-125495.
In order to further reduce the sizes of the devices and enhance the performance, improve the accuracy and reduce noise generated from the devices, it has been required to further reduce the size, enhance the output, improve the rotational accuracy and reduce the manufacturing cost.
In order to enhance the output and reduce the vibration and noise so as to meet the requirements, a technique to suppress the generation of cogging torque by combining a stator, which is formed out of 12 salient-pole-cores, with 10-pole-magnetized rotor (or 14-pole-magnetized rotor) is disclosed, for example, in Japanese Patent Unexamined Publication No. H8-8764. According to the technique disclosed in this patent publication, it is possible to realize high output, low vibration and low noise by suppressing the generation of cogging torque.
However, it is necessary to arrange 3-phase windings, which are wound by concentrated winding, as follows. It is necessary that a first winding, which is arranged at a position of 180° of the mechanical angle, and a second winding of the same phase are arranged being wound in different directions so that they can be unlike poles from each other. Further, it is necessary that the first winding and a third winding of the same phase, which are adjacent to each other in the circumferential direction, are arranged being wound in different directions so that they can be unlike poles from each other. Further, it is necessary that a winding of a different phase adjacent in the circumferential direction is arranged being wound in the same direction as that of the third winding. As described above, the winding and the processing of connection become complicated.
Problems to be solved are described as follows. The three-phase windings must be arranged in such a manner that a combination, in which the winding directions of the 3-phase windings of the same phase are opposite to each other, is repeated and that the different phase windings adjacent to each other are of the like pole. Accordingly, the winding work becomes very complicated and it is difficult to automatize the winding work. Therefore, a conventional stator manufacturing apparatus can not be used. Therefore, it becomes necessary to make a new investment in equipment or modify a conventional winding apparatus. As a result, the manufacturing cost is raised.
In the case of 3-phase-Y-connection in which the same phase windings are connected only in series, when the concentrated winding is continuously made by using crossover lines without cutting the windings of the same phase, it becomes easy to conduct the connection processing. However, the following problems are caused in the winding work to obtain a high output. That is, it is necessary to employ a thick wire, the diameter of which is large. Accordingly, it is difficult to conduct concentrated wiring while the winding direction is being changed. As a result, a space factor of the slot of the wiring is lowered and the efficiency is deteriorated.
On the other hand, when a thin wire, the diameter of which is small, is employed and the same phase windings are connected to each other by the 3-phase-Y-connection not only in series but also in parallel, it is possible to prevent the space factor of the slot from deteriorating. However, the wire connection work becomes complicated.